Should you worry about whether your cat is making you crazy?

Here is a guest post by UC Berkeley junior Alex Martin who is working with us on a study of the Berkeley Animal Shelter

It’s no secret that animals — including humans — serve as a nutrient-rich reservoir for microorganisms. And while the grooming habits of felines may have earned them a reputation as refreshingly clean, just like any other pet, household cats introduce unwanted microorganisms into the homes of their owners. Many of these are harmless or not transmissible to humans; a few are not. One belonging to the latter group is the Toxoplasma gondii, a protozoan that infects cats, humans, and a host of other species (sea otters, dogs, mice, basically all mammals), causing Toxoplasmosis.
Though there is evidence to suggest that a surprisingly high percentage of people have been exposed to the protozoan, healthy individuals are usually asymptomatic and may be unaware that they have been infected. Individuals with compromised immune systems, such as infants and people with HIV/AIDS, may develop flu-like symptoms. Rarely, people experience seizures and fatal brain damage.
Though clinical symptoms are rare, there is evidence to suggest that people with latent infections are more likely to die in car accidents and behave impulsively. One study released earlier this year lends support to earlier studies, identifying a link between childhood cat ownership and the development of schizophrenia later in life.
If these things seem reason enough to immediately cease all contact with cats, however, there are a few things to note. Firstly, no one has been able to prove that Toxoplasma gondii — let alone cat ownership — causes car accidents, impulsiveness, or mental illness. As of now, they are merely correlated. Secondly, people are infected with the Toxoplasma parasite all over the world — including places in which people don’t keep cats as pets. The protozoan can be found on undercooked meat and unwashed produce, and gardeners or young children who dig in the soil where a cat has buried its feces are also risk.
Instead of trying to avoid exposure at all costs, then, perhaps we should work to better understand Toxoplasma gondii, and to establish the nature of its connection (or lack thereof) to mental illness and maladaptive behaviors. An in-depth study of the parasite seems to be a promising way to further our understanding of human health through the lens of the felids.